OF CERTAIN ELECTRICAL SUBSTANCES. 
169 
upper coating c with the electrometer, a quantity equal to five measures was depo- 
sited on it, and the intensity taken under the common conditions of the Leyden ex- 
periment. In this case, however, the intensities varied considerably, being different 
with each substance, as shown in the following Table : — 
Table I. 
Showing the Intensity of five measures of electricity in degrees of the Electrometer 
when accumulated as a charge on different coated Electrics. 
Substance. 
Lac. 
Brimstone. 
Best Flint Glass. 
Bees’ wax. 
Pitch. 
Rosin. 
Air. 
O 
2 
O 
O 
2*5 
3-25 
O 
4 
O 
5 
O ; 
32 
Intensity. . 
2-25 
When ten measures were deposited, the intensities were found to increase as the 
square of the quantity, according to the law already referred to (11.) ; so that with 
ten measures the small differences were more marked. 
13. It is not difficult to discover from these intensities the indirect induction or 
specific inductive capacities of the various substances to which they refer, since their 
respective influences over the amount of induction which takes place through them, 
may be conceived to vary with the quantity of electricity condensed, as it were, by 
the uninsulated coating, and thus rendered insensible to the electrometer. 
Now, by the known laws of the electrometer*, the intensity of the charged side 
is proportional to the square of the quantity which the free coating ceases to hold 
in equilibrio ; we may therefore find this quantity, and having deducted it from the 
whole quantity of charge, the remainder may be taken to represent the inductive ca- 
pacity of the substance under examination. 
Thus, to find the inductive capacity of lac with reference to five measures by 
Table I., we have to find the free quantity corresponding to an intensity of 2°. But 
the intensity corresponding to one measure, taken as a free quantity, is 4° (Exp. 1.). 
Taking then the quantities as the square roots of the intensities, we obtain *7 of a 
measure nearly for an intensity of 2°, which is the uncondensed part of the charge T- 
If, therefore, we subtract this from five, the whole number of charges, we have 4*3 
for the indirect induction, or specific inductive capacity of lac. In a similar way 
we find the relative specific inductive capacity of air to be 2 ’ 2 , of pitch 4 , and so on, 
as in the following Table. 
* Philosophical Transactions for 1839, p. 237. 
t Or by the laws of the electrometer, we have in taking the forces as the square of the quantity 4° : 2° : : 1 2 : x- 
or 4 x % = 2, and x = V -5 = *7 nearly for the quantity corresponding to 2° when the quantity corresponding 
to 4° is unity. 
MDCCCXLI1. 
Z 
